It is known to use powder dosers with a variety of means of controlling powder flow rate to dispense powder for pharmaceutical purposes. For the purpose of this application powder is defined as a ‘finely divided solid’. It is important that the correct amount (mass) of powder is provided to the end consumer in order that the drug has the correct efficacy and is safe.
Many existing powder dosers use volumetric systems for measuring powder which are fast, but whose accuracy may be compromised if the powder density varies from that expected.
Volumetric systems typically suffer from poor dose to dose accuracy and the mean weight can often be in error relative to the target weight.
Gravimetric systems weigh powder as it is being filled directly into a product or into a receptacle for subsequent transfer. Gravimetric systems can be very accurate but are traditionally considered too slow for production. Gravimetric systems are considered slow because of the time taken to weigh, combined with the variability in powder flow characteristics.
Many powder dosers have an aperture through which powder is released with a closure to control powder flow rate through the aperture. Such arrangements can lead to problems with durability, as closures can cause wear around apertures after repeated opening and closing cycles. Using harder materials that would increase durability can lead to degrading performance with time as powders stick to and clog the internal surfaces.
U.S. Pat. No. 7,284,574 discloses a system in which a hopper containing a reciprocating stirrer is used to improve powder flow rate and dispensing speed. A problem with this system is that the design of the stirrer and its reciprocating nature means that a significant proportion of the powder in the hopper can be left unstirred, and may therefore remain in the hopper.
It is desirable to provide a powder doser which can accurately and consistently dispense a range of quantities of powder at a suitable speed. It is further desirable to provide a system capable of dispensing each dose into individual containers. Such a system may include a transfer system for this purpose due to the nature of some multi-dose packaging or containers which do not facilitate the weighing of individual doses.